Updated ThirdParty/ReadMe

ThirdParty/ReadMe.md

-### Logging with logog ###
+# Third-party libraries #
+
+## logog ##
 
 For details how to use logog see the [OGS devguide](http://devguide.opengeosys.com/logging/) and the [logog documentation](http://johnwbyrd.github.com/logog/).
 
@@ -9,3 +11,15 @@ For details how to use logog see the [OGS devguide](http://devguide.opengeosys.c
 It was initially integrated with:
 
     git-subtree add -P ThirdParty/logog --squash https://github.com/johnwbyrd/logog.git master
+
+## RapidXML ##
+
+Is used for XML-IO. Is integrated directly.
+
+## tclap ##
+
+Command line option parser. Is integrated directly.
+
+## zlib ##
+
+Compression algorithms. Is integrated directly.
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